Rotary electric current interchange contact



Sept. 25, 1962 ROTARY ELECTRIC CURRENT INTERCHANGE CONTACT R. W. BETH KE 2 Sheets-Sheet 1 Filed Oct. 19, 1959 Fig.

llhllmu I7 IN V EN TOR. Pay m and 2M Seth/4? Sept. 25, 1962 R. w. BETHKE ROTARY ELECTRIC CURRENT INTERCHANGE CONTACT Filed Oct. 19, 1959 2 Sheets-Sheet 2 INVENTOR. Raymond ZM Bet/2K6 BY fittorngr atet Patented Sept. 25, 1962 fire This invention relates to electric contacts and more particularly to means for transferring current of large magnitude between conductive components which coact ro- .tatably in electrical apparatus.

This application is related to application Serial No. 505,293, filed May 2, 1955, and which is now abandoned.

In circuit breakers, switches and other electrical devices, it is often necessary to transfer current between components which are mechanically interconnected but free to execute a predetermined rotary movement with respect to each other. For example, in a load interrupter or an ordinary disconnect switch it is often necessary to transfer current from a swinging blade to a blade support through a poorly conductive hinged joint. As a result, a high resistance junction may develop between said movable parts which manifests itself in the form of heat and excessive voltage drop.

The prior art demonstrates a variety of means for mitigating the aforementioned effects by paralleling such high resistance junctions between movable parts through the media of flexible shunts, cam and follower arrangements and direct wiping contacts. Moreover, in hinged joints various means of achieving high pressure contact have been used, such as biasing means, in an effort to minimize contact resistance between them. Such prior art methods are not fully satisfactory, however, because they frequently deteriorate after prolonged use and because they are costly, intricate and difiicult to incorporate where space limitations are an important factor.

A general object of this invention is to overcome the above indicated defects by providing a novel and eflicient means for transferring current through rotatable joints between movable components of electrical apparatus.

ther more specific objects are to provide a current transfer contact which is simple in form and easily manufactured and installed; to provide a contact which is endowed with inherent ability to compensate for wear, if any; to provide a contact which offers only infinitesimal sliding friction between members; to provide a contact which is versatile in that it may be used effectively with both coaxial and parallel members; to provide a contact which may be conveniently ganged or stacked for accommodation of large magnitude currents; and to provide a contact which is self-aligning so that seizing or binding of parts is avoided.

Another important object is to provide a current transfer contact which increases its bearing pressure through self-generated electromagnetic efiects when subjected to inordinate current flow.

These and other objects and advantages of the invention will become apparent from the detailed description of the invention taken in view of the accompanying drawings which show:

FIG. 1 is a sectional view of a hinged joint incorporating the invention;

FIG. 2 is a top plan view with parts broken away of the hinged joint shown in FIG. 1;

FIG. 3 is a sectional view of a hinged joint incorporating an alternative form of the invention;

FIG. 4 is a sectional view of a hinged joint incorporating an alternative embodiment of the invention; and

FIG. 5 is a top plan view with parts broken away of the hinged joint shown in FIG. 4.

In general terms, current interchange according to the invention is accomplished between relatively rotatable members through the agency of a coil spring. In the preferred form, the spring comprises a toroid disposed in an annular channel having a depth less than the helical diameter of the spring so that all convolutions of said spring are inclined in a single direction. As a result, the inclined convolutions obtain their contact bearing pressure from their tendency to straighten out or to assume their unstressed shape. Current transfer is effected through a large number of parallel paths comprising the spring convolutions from the inner to the outer periphery of the toroid defined by the spring.

When utilizing a spring contact to transfer current between relatively rotatable members the design of the spring will depend to some extent upon the direction of current transfer. For example, FIGS. 1 and 2 illustrate how current may be transferred between relatively rotatable parallel members 11 and i=2 hinged together by means of a pivot bolt [l4 which passes through complementary apertures formed in the ends of each of said members wherein current is transferred in a direction parallel to the pivotal axis represented by the center line of pivot bolt 14. Here, the individual convolutions of the current interchange spring 16 are inclined in planes which intersect the pivotal axis at an oblique angle. This is accomplished by confining spring 16 in a direction parallel to the pivotal axis of parallel members 11 and 12.

More specifically, in the embodiments of FIGS. 1 and 2 current interchange spring 16' is disposed in an annular channel 18 formed in member 11 and which is coaxial with pivot bolt 14. The upper margin of channel 18 is defined by the planar surface of member 12 which is held in position by pivot bolt 14. Because the depth of groove 18 in a direction parallel to the pivotal axis is less than the helical diameter of spring 16, individual convolutions of said spring are forced to lay over in planes which intersect the pivotal axis at an oblique angle. As a result of the springs tendency to assume its natural or uncompressed state each of the spring convolutions tangentially engages the lower surface :19 of member 12 and the lower surface 20 of groove 18. As a result, each of the convolutions of spring 116 provides an individual current path between members 11 and 12. While channel 18 is shown to be formed in member 11, it will be understood that it may be provided in any convenient manner.

In order to allow members 11 and 12 to be rotated in both directions relative to the inclination of spring 16, it is preferable that the angle of layover be such that the friction force between the spring and surfaces 1'9 and 20 plus the existing stress on the spring, is not sufiicient to reverse the direction of layover and thereby permanently distort the springs or to jam the convolutions between the members when rotation is against the angle of layover.

It is also important to consider the ratio of the mean diameter of the spring convolution to the diameter of the spring wire. It has been found that when this ratio is less than 10, springs wound with wire diameters larger than 28-thousandths of an inch have a tendency to become stiff. However, slightly smaller ratios are acceptable when smaller wire sizes are used. Excessively stiif springs are undesirable because they increase the difficulty of assembly and also the lateral pressure between members which results in excessive wear.

By utilizing a current interchange spring according to the invention, a multiplicity of relatively low pressure current interchange points which are uniformly distributed about the axis of rotation is achieved whereby static seizure or peak frictional drag between the members is substantially eliminated. In addition, this large number of cur-- rent interchange points substantially reduces the necessary contact pressure between members. This is contrasted with prior art high pressure contacts, wherein only a few points of current interchange are achieved necessitating very intense frictional engagement between the members. It will be appreciated that this latter condition is highly undesirable in electrical switches and circuit interrupters wherein rapid initial acceleration is extremely imperative.

In addition, the distributed, relatively low pressure contacts of the instant invention reduce wear and is self-aligning so that the likelihood of failure is also substantially reduced. Also, by providing a plurality of parallel current interchange points the resistance between members is substantially reduced thereby reducing the heating inherent in prior art joints.

FIG. 3 illustrates how extremely large magnitude currents may be transferred utilizing the parallel current interchange principle. Here, current is transferred from a pair of parallel outside members 11 and 31 to a central member 12. Outside member 11 is provided with a pair of concentric channels 18 and 18 which are coaxial with pivot bolt 14 and in which current interchange springs 16 and 16 respectively are disposed. Similarly, current interchange springs 36 and 36 are disposed in channels 38 and 38' formed in the other outer member 31. Current is transferred between outer members 11 and 31 and the central member 12 through each of the convolutions of current interchange springs 16 and 16 and 36 and 35. It will be understood that while four current interchange springs are shown in the embodiment of FIG. 3 this is merely intended as an example, the actual number being determined by the current requirements of the junction. Also, while adjacent springs 16 and 16 and 36 and 36 are shown to be disposed in individual channels they may be disposed in the same channel by reversing the angle of layover of adjacent springs so that the individual convolutions will not intermingle.

FIGS. 4 and illustrate how current may be transferred between rotatable members which are radially related. For example, in the illustrated embodiment current is transferred between a central shaft 40 and a radially extending arm 41 which has an integral collar 48 coaxially disposed around shaft 40 and journaled for rotation on surfaces 49 and 50. Here, current interchange spring 42 is disposed in an annular groove 44 formed around the periphery of the central member 40 and whose outer margin is defined by the inner surface 46 of a collar 48. An annular shoulder 51 and a retaining plate 52 hold collar 48 in the correct axial position relative to shaft 40.

The radial depth of groove 44 is less than the helical diameter of spring 42 so that the individual convolutions of said spring are forced to lay over in planes which are parallel to the axis of rotation of collar 43. The tendency of the spring 42 to assume its original unstressed shape forces each of the individual convolutions into engagement with surface 46 of collar 48 and the inner surface 54 of groove 44. As a result, each individual convolution provides a parallel current path in a radial direction between the central member 40 and outer member 48.

Here again, if it is desired to transfer high magnitude currents a plurality of interchange springs may be utilized.

While only a few embodiments of the invention have been shown and described, it is intended to cover in the appended claims all modifications thereof that fall within the true spirit of the invention.

I claim:

1. In combination, a pair of conductive members having nominally parallel portions, means for holding said portions in a side by side opposed relation, said means permitting relative rotation between said members about a common axis which intersects the plane of each of said portions, said means preventing axial separation of said portions, a helical wire wound spring contact disposed between said portions, and in engagement therewith, said means maintaining the distance between said portions at a value which is less than the normal outside helical diameter of the convolutions of said spring to confine the latter in inclined planes which intersect the rotational axis of said members at an oblique angle so that a component of force is generated in each convolution for developing a wiping contact between spaced apart points on said convolutions and the rotatable members, whereby substantially each convolution provides a current path between said portions so that the total contact pressure necessary to provide current transfer between said portions and said convolutions is relatively small.

2. Current interchange structure comprising a pair of conductive members, each of said members having a surface, fastening means connecting said members for relative rotational movement about an axis of rotation, said fastening means holding said surfaces in an opposed relation, and a helically wound conductive spring contact disposed between said surfaces, said fastening means preventing axial separation of said members so that the distance between said surfaces is maintained at a value which is less than the normal convolutional diameter of said spring contact, the resiliency of said spring contact holding substantially all of its convolutions in uniformly advancing spiral relation with each other and in electrical engagement with each of said surfaces, the locus of points of contact between convolutions of said spring and each of said surfaces being circular and concentric with said axis of rotation.

3. Current interchange structure comprising a pair of conductive members, each of said members having a surface, coupling means holding said surfaces in an opposed relation and permitting rotational movement of said members about an axis of rotation, a helically wound conductive spring contact disposed between said surfaces and in a concentric relation to said axis, said coupling means preventing axial separation of said members to maintain the distance between said surfaces at a value which is less than the normal convolutional diameter of said spring contact so that the resiliency of said spring holds substantially all of said convolutions in electrical engagement with each of said surfaces and in uniformly advancing spiral relation relative to each other, whereby substantially each of said convolutions provides a current path between said surfaces so that the contact pressure necessary to insure current interchange is relatively small and the frictional drag between said convolutions and said surfaces is minimized, the locus of points of contact between the convolutions of said spring contact and each of said surfaces being substantially circular and coaxial with said axis.

4. Current interchange structure comprising a pair of conductive members, each of said members having a surface, said surfaces being disposed in an opposed relation, pivotal coupling means engaging each of said members, said coupling means connecting said members for pivotal movement about an axis, a helically wound conductive spring contact disposed between said surfaces, said coupling means preventing substantial axial movement of said members and holding said surfaces in an opposed relation with the distance between said surfaces maintained at a value less than the normal convolutional diameter of said spring so that the resiliency of said spring holds substantially all of its convolutions in good electrical engagement with each of said surfaces and in uniformly advancing spiral relation with each other, the locus of points of contact between the convolutions of said spring and each of said surfaces being substantially circular and concentric with said axis, and annular means for holding said spring means in a concentric relation therebetween.

5. In combination, a pair of conductive elements that are relatively rotatable about a common axis, said elements having nominally parallel portions which are adjacent to each other, a surface formed on each of said portions in opposed relation to each other, a helically wound spring contact disposed between said surfaces and encompassing said axis, holding means engaging each of said members for preventing the axial separation of said surfaces to maintain the distance between said surfaces at a value which is less than the normal outside helical diameter of the individual convolutions of said spring so that said convolutions are inclined relative to said surfaces, the resiliency of said spring contact holding spaced apart points on said convolutions in firm electrical engagement with each of said surfaces, whereby substantially each of said convolutions provides a current path between said portions so that the total contact pressure necessary to insure current transfer is substantially small and the frictional drag between said portions and said convolutions upon relative rotational movement between said members is minimized, and annular means surrounding said spring contact means for holding the same in a substantially concentric relation relative to said axis.

6. In combination, two conductive members which are relatively rotatable about a common axis, said members having spaced apart surfaces disposed in a substantially parallel relation, a resilient, helical wire wound spring contact disposed between said members and in contact with said surfaces, holding means for preventing axial separation of said surfaces to maintain the distance therebetween at a value less than the normal outside helical diameter of the convolutions of said spring contact so that said convolutions have their planes inclined relative to said surfaces with spaced apart points on the individual convolutions in 6 firm electrical contact with each of said surfaces to form a multiplicity of current paths between said members, the locus of the points of contact between said convolutions and each of said surfaces being substantially circular, and annular means for retaining said spring contact between said surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 1,873,042 Rohrdanz Aug. 23, 1932 2,154,275 Linn Apr. 11, 1939 2,193,122 Crabbs Mar. 12, 1940 2,359,055 Schwager et a1 Sept. 26, 1944 2,379,047 Thomas June 26, 1945 2,948,794 Fjellstedt et a1 Aug. 9, 1960 FOREIGN PATENTS 128,148 Australia June 29, 1948 685,738 Germany Dec. 23, 1939 29,822 Great Britain Mar. 1, 1957 186,526 Great Britain Oct. 5, 1922 774,419 Great Britain May 8, 1957 OTHER REFERENCES PV Air Switch Bulletin, PSE2, page 5, April 1957. 

